Furfural solvent separation of aromatics from liquid mixtures



May 5 1954 G. a. ARNOLD l-:TAL 3,132,093

F'URF'URAL SOLVENT SEPARATION OF' AROMATICS FROM LIQUID MIXTURES Filed Jan. 26, 1961 `'George B. Arnold, Fishkill,

drocarbons. Vseparation fof naphtlialene ,and naphthialene precursors',

arcanes FURFURAL SLVENT SEPARATIN OF AROMATICS FPAM LEQUD MHXTURES Pleasantville, N.Y., assignors to Texaco Inc., New York,

N.Y a Corporation of Delaware Filed Jan. 26, 1961, Ser.' No.` 85,151

Claims. (Cl. 20S- 320) This invention relates to the separation of liquid mixtures with a selective solvent. More particularly, it relates tothe separation of aromatic hydrocarbonsfrom lmixtures with other hydrocarbons by solvent extraction with fur-k fural followed by azeotropic distillation ofthe extract.

solvent mixture. In one embodiment 'of thisinvention, naphthalene and alkyl naphthalenes are separated from gas oils by selective solvent extraction with furfural and and Howard H. Gross, y

l United States -Patent ice l ing a major portion ofthe aromatic hydrocarbons and the remaining nonaromatic hydrocarbons, and atleast a part of said extract mix is distilled in a distillation zone in the presence of furfural reflux and added Water vapor (steam) effecting separation of an azeotropic mixture comprising water, -nonaromatic hydrocarbons and furfural from an aromatic rich bottoms fraction.

'An advantage of thel process of this invention is that aromatic concentrates containing more than 80 percent aromatics may be separated from gas oil boiling range hydrocarbons with furfural employing temperatures about usual ambient atmospheric temperatures and moderate solventrates;l

Another advantage of thel process ofthis invention is that a single solvent is employed as both a selective solvent in an extractionV step and asa component ofthe azeo- V tropic mixture-in an azeotropic distillation'step.

the dissolved aromatics are concentrated and separated by a highly selective azeotropicdistillation employing furfuralas reflux. Y Y

Gas oils from some aromatic crude sources and gas oils from thermal and catalytic cracking containingsubstantial quantities of useful aromatic hydrocarbons, for examplepbenzenoid, naphthalene, and naphthalenic hy- This invention is particularly useful in the that ian'aphthalenic hydrocarbons which mayhbe converted to naphthalene, for example, by hydrodealkylation. These desirable aromatics are diluted with nonaromatic hydrocarbons of the same `boiling range making their separation by simple distillation impossible.v It is` an object of this invention to separate aromatic hydrocarbons in concentrated form from mixtures with nonaromatic hyrocarbons. Other objects will'be apparent fromthe following description and claims.

Solvent extraction is a well known process for the separation of aromatic hydrocarbons from mixtures with nonaromatic hydrocarbons of similar boiling range. 'Furfural has been found'to be an excellent'selective solvent in the separation of hydrocarbons of relatively high boiling point, for example, hydrocarbons useful in the `manufacture of lubricating oils and catalytic cracking feed stocks. Fur'fural extraction has .alsobeen found useful in the manufacture of ykerosine an'dlow boiling gas oil productswhere a raiiinate of low aromatic content is produced.

However such lower boiling hydrocarbons, for example,

those boiling within the range of 400 to 600 F. are considerably more soluble in furfural than lubricating oils or For the separation of aromatics in a concentration above 80 percent, high, solvent selectivity is necessary which in turn requires temperatures far below usual ambient atmospheric temperatures, for example, about 30 F. At these low temperatures the solvency of the furfural is substantially reduced so that `high solvent ratios, for example,

^ about 250 percent` orhigher are required to obtain acceptable yields. Y t n In accordance with this invention, a liquid hydrocarbon n mixture containing aromatic and nonaromatic hydrocarbons is-contacted with liquid furfural effecting formation of a rainate mix comprising a major portion of the nonaromatic hydrocarbons and an extract mix` comprising a yfurfural phase containing dissolved hydrocarbons includ- The accompanying drawing-diagrammatically illustrates I one form of vthe process of Ythis invention. Althoughthe `0.256 pound per square inch absolute.

drawing illustrates one arrangement of apparatus in which the process of this invention may be practiced, it is not intended to limittheinvention to the particular materials or apparatus described.

A gas oil feed is passed through line linto'extraction jtower 11. In tower ll the `oil feed is contacted `with liquid furfu'ral in countercurrent ilow. The furfural solvent may be .dry? that is substantially free of `dissolved water or Wet that is containing some `dissolved water as is well known in the art of solvent extraction with furfural. Furfural is introducedinto-tower 1l throughV line 2 at a rate of about i120 to 300 volume percent of thev loil feed. In extraction tower 11V aromatic components ofthe-.oil feed are preferentially dissolved inthe furfural and aromatic rich extract mix is withdrawn romthe bottom of `tower 11 through line 3. Rainate oil denuded of aro- `50 F. and preferablywithin the range of about 20 to 30 F. is maintained in tower 11. A desired-temperature gradient may be maintained by heating the furfural passed to the top of the tower in-exchanger 5 and cooling the bottom ofthe tower with water in coil 6. Desirably the temperature of the tower bottom is maintained as low as possible with cooling water, for example-about to F.- When ambient atmospheric temperatures and dew. points are too high to obtain cooling Water of desired temperature from a conventional cooling tower-or spray v pond, the cooling water may be chilled by vacuum flashing, for example, water may becooled to 60 F. by discharge to a vacuum zone maintained at a pressure ,of

Extract mix is passed through lines 3, 14, `and l5, prerheater v16, and line 1'7 to extnact-.azeotrope tower 18. Tower l18 `comprises a fractionalV ydistillation tower provided with a reboiler 2.0. Steam is introduced through tand provide the water redrocarbon, furfural, `and Water. This taze'otrope is removed as overhead vapor from .tower-18 through line 22. The formation of a hydrocarbon-water-furfural azeotrope permits separation of all of the furfural and water and 'la pant .of thehydrocarbons 'as overhead products leaving r-tlle remaining hydrocarbon extract 'as` bottoms. Additionally, the presence of fut-tural enhances the relative volatility of non-aromatic hydrocarbons I`as compared with the aromatic hydrocarbons so .that thenonaromatic `hydrocarbons `appear in the azeotropic` mixture taken overhead and the aromatics are concentrated in the bottoms. Aromatic concentrate is' removed tower18 through line' 24.

from the bottom of y Azeotrope vapors 'from tower 18 are disch-arged .through level at interface 33 and yis confined by wei-r 31. Furi f-ural -iayer is withdrawn through line 34 and a part is returned asreflux to tower 18 through line 2,3. The intermediate phase is v.predominantly water and contains a small amount of dissolved furfur-al and oil. The Water layer has a lower level at interface 33 and an upper layer -at interface 32. The water ylayer overflows Weir 31 and is confined by weir 30. Water phase is withdrawn through line `35. The upper layer having a lower level Iat interface 32is predominantly oil and contains a small amount of dissolved furfural and water. The oil phase I overflows weir and is withdrawn through line 36. Oil withdrawn through line 36 is similar to the raffinate discharged through line 4 and may be combined with it before or after separation of dissolved furfural. Y

,Furfunal phase withdrawn through line 34 may be passed through lines 37, and 38 to provide the solvent introduced into tower 11 through line 2. In this case the furfural will `have a water content established by the equilibrium at the temperature and conditions-of separator 27. lf it `is desired to control the water content of the ffurfural recycle stream at a lower value independently of the temperature of separator 27,"the furffural may be dried by distillation in which a binary azeotrope comprising furfural sand substantially all of the dissolved water is removed overhead `from the remaining dry tortural. In this case, part or all of the wet furfural in line 37 is passed through line 40 to tower 41. Tower 41 is provided with a reboiler 42. Dry fur-foral is withdrawn through line 43 and returned to line 3S. Vapor K comprising furfural and water with a small amount of oil lis withdrawn through linesV 44 and 45, condensed in Vcondenser 46, and `the resulting condensate is passed through line 47 to separator 50'. Y

Water phase containing dissolved furfural can also be freed of fur-fural by distillation since the azeotrope of water and furfural is lower` boiling than either furfural or water. In this case an azeotrope containing all yof the yfurfural and some 'of the Water is removed overhead from the remaining ff-urfural-free water which is withdrawn as trope is formed, substantially. less steam is required to satisfy the azeotrope composition with savings in utilities costs. Preseparation of a part of the furfural also provides Ial means of [controlling the amount of azeotrope formed and in turn of controling the amount of nonaromatic toil separated in the azeotropic distillation. rThis preseparation of furfural is effected by passing at least a pant of the `extract-mix in line 3 through line 70, heat 'exchanger 71 'and line 7 2 into solvent flash tower 73. In tower 73, a Ipart lof the furfural in the extract-mix is vaporized and withdrawn `through line 74. These vapors are combined with the vapors in line 22 for condensation .and phase separation. Extract-mix partially denuded of furfural is withdrawn through line 75 and passed through line 15 to extractftower `18. Solvent fiash tower 73 may .be operatedfindependently of the pressure'of extract azeotrope tower v18 by providing separate' vapor recovery facilities, not shown. In the latter case, solvent flash tower 73 may be operated at a lower pressure or advantageously under a vacuum to effect increased separation of solvent.

Y High extraction yields, for example, in excess of about 90 percent of the aromatics contained in the gas-oil feed are obtained inthe extraction stepvof this process. High `extraction yields are favored by high solvent ratios and relatively high extraction temperatures. At high extrac- .tionyield levels, because of the lower solvent selectivity at conditions favoring high yields, a substantial amount of nonaromatic hydrocarbons is also extracted so that the concentration of aromatics in the, extracted hydrocarbon is at least 70 percent and preferably within the range of about 80 to 85 percent. Since most of the aromatics are included in the extract, the raffinate contains very little aromatic hydrocarbon and is therefore particularly valuable in the manufacture of heating oils, Y.diesel fuel oils, catalytic cracking feed stocks and other products where aromatics are undesirable.

In the azeotropic distillation step, the concentration of aromatics in the extract is increased to about 90 percent or higher by selectively removing nonaromatic hydrocarbons. The azeotropic distillation is effected at a top tower temperature of about 290 to 300 Fand with a bottom tower temperature of about 400 to 450 F. Some i ,extract vaporization in the azeotropic distillation tower bottoms. Water phase from separator 27 is withdrawn through lines 35, and 51, to -water distillation tower 53. Steam is introduced into tower 53 through line 54.l Water free of furf-ural is discharged from the bottom of tower 53 through line 419.

is discharged through line 55 and combined with the similar mixture in the line 44 from tower 41 Ifor condensation and separation.

Vtower 11. Water phase between interfaces 60 and 62 overflows Weir 57 but is confined by weir 56. Water phase is withdrawn through line 63 and combined with the water trom line 35 for furfural separation in water distillation towerv 53. Oil layer separating above interface 62 overflows weir 56 and is withdrawn through line 64. This oil may be combined with oil in line 36 or 4 lfor Ifurfural separation and recovery, not shown.

A part of the furfural in the extract-mix may be separated prior to the iazeotropic distillation and thereby substantially reduce the amount of azeotrope which must be separated as an overhead product. `Since less azeo- Overhead vapor from tower53, y comprising water, furfura-l,V and a small amount of oil,

reboiler is desirable to provide the heat required in vaporizing the azeotrope Vseparated Vas an overhead product. Steam is added at the bottom of the azeotropic distillation tower `at, a rate of about 0.1 pound per pound `of extract mix to satisfy the composition required to form ,the azeotrope and to assist in the distillation and the `stripping of Yfurfuralfrom the extract bottoms product. Furfural rich phase, separated from the condensed azeotrope distilled overhead, is returned to the azeotropic distillation tower as reflux to provide rectification of the hydrocarbons'rising in the tower effecting-stripping of the aromatic constituents therefrom.

Example `In accordance with the process of this invention, a gas oil produced by catalytic cracking is treated for recovery `of aromatics. The catalytic cracked gas oil charge stock jhas the following tests:

' YThe gas oil charge'is contacted at a rate of 2500 barrels per day (b.p.d) with furfural in a countercurrent contactor at a solvent dosage of 175 volume percent.` A temperature gradient of 40 F. is maintained in the; COIlCfOr With the top temperature (raffinate) of l201 aisance F. and bottom temperature (extract) of 80 F. Rainate mix is stripped to separate dissolved furfural and produce a ra'inate product in a yield of 47.3 volume percent of the charge oil.

.Extract mix is flashed effecting vaporization and separation of 70 percent of thefurfural producing a flashed extract mix containing 37 percent furfural. Flashed extract mix at a rate of 2673 bpd. is passed to a distillation column. Exhaust steam at a rate of 95,080 pounds per day is introduced into the tower bottom and the top of the tower is reuxed with furural to maintain a top tower temperature of 300 F. An azeotrope is distilled overhead containing furfnral, the steam introduced Vinto the tower bottom and I367 b.p.d. of hydrocarbon. Aromatic concentrate is withdrawn from the bottom of thc tower at a rate of 1317 b.p.d. The composition of the aromatic concentrate is 94 percent aromatics, 5 percent parafl'ins and l percent naphthenes. The aromatic concentrate contains 90.0 percent ofthe aromatics contained in the catalytic cracked gasoil feed.

We claim:

1. A vmethod for the separation of an aromatic rich fraction froma liquid hydrocarbon mixture which comprises contacting said mixture with a solvent comprising `liquid furfural effecting formation of a raflinate mix comprising a hydrocarbon phase containing dissolved furfural and an extract mix comprising a furfural phase containing dissolved hydrocarbons consisting of 70 to 85 percent aromatic hydrocarbons, distilling at least a part of said extract mix in a distillation zone in the presence of a reflux as hereinafter provided and added steam at a rate of about 0.1 pound of steam perpound of extract mix passed to said distillation zone into an overhead vapor comprising Water, hydrocarbon and furfuralV and a bottoms liquid consisting of said aromatic rich yfraction containing at least 90 percent aromatic hydrocarbons, condensing said overhead vapor forming a hydrocarbon rich phase, a water rich phase and a furfural rich phase, separating said hydrocarbon rich phase, said water rich phase and said furfural rich phase, and passing at least a portion of said furfural rich phase as-said reflux to said distillation zone.

v2. The process of rclaim A1 wherein said liquid hydrocarbon mixture is a gas loil produced by catalytic cracking.

3. The process of claim 1 wherein said extract mix is flashed under conditions effecting vaporization and separation of a part of the furfural contained therein and the resulting extract mix partially denuded of furfural is pas-sed to said distillation zone.

4. A method for the separation of an aromatic fraction containing at least 90 percent by volume of aromatichydrocarbons from a catalytic cracked gas oil which comprises contacting said gas oil with a liquid solvent comprising furfural at a solvent ratio within the range of about 120 to 300v volumes of solvent to 100 volumes of said gas oil in a solvent extraction zone, withdrawing extract mix comprising furfural and dissolved hydrocarbons consisting of to 85 percent aromatic hydrocarbons from said extraction zone at a temperature Within the range of about to 100 F. While maintaining a temperature gradient through said extraction zone less than about 50 F., passing at least a part of ySaid extract mix to a distillation Zone in contactwith a reflux as hereinafter provided and added steam at a rate of about 0.1 pound of steam per pound of extract mix passed to said distillation zone, distillatively separating an overhead vapor comprising an azeotrope of water,

furfural and hydrocarbon from a bottoms product com' prising aromatic hydrocarbons of at least percent by volume purity, condensing said overhead vapor forming an oil-rich phase, a Water-rich phase and a furfural-rich phase, and passing at least a portion of said furfural rich phase as said reflux to said distillation zone.

5. A method for the separation of an aromatic rich fraction from a liquid hydrocarbon mixture which cornprises contacting said mixture with a solvent comprising liquid furfural eifecting formation of a raiinate mix comprising a hydrocarbon phase containing dissolved furfural and an extract mix comprising a furfural phase containing dissolved hydrocarbons consisting of 70 to 85 percent aromatic hydrocarbons, heating said extract mix vaporizing a part of the furfural in said extract mix, separating furfural vapor from remaining liquid extract mix, passing said remaining liquid extract mix to a distillation zone, distillatively separating said remaining liquid extract mix in said distillation zone in the presence of a reux as hereinafter provided and added steam at a rate of about 0.1 pound of steam per pound of extract mix passed to said distillation zone into an overhead vapor comprising water, hydrocarbon and furfural and a bottoms liquid consisting of said aromatic rich fraction containing at least 90 percent aromatic hydrocarbons, condensing said overhead vapor forming a hydrocarbon rich phase, a Water rich phase and a furfural rich phase, separating said hydrocarbon rich phase, said water rich Y phase and said furfural rich phase, and passing at least a portion of said furfural rich phase as said reux to said distillation zone.

References Cited in the le of this patent l UNITED STATES PATENTS 

4. A METHOD FOR THE SEPARATION OF AN AROMATIC FRACTION CONTAINING AT LEAST 90 PERCENT BY VOLUME OF AROMATIC HYDROCARBONS FROM A CATALYTIC CRACKED GAS OIL WHICH COMPRISES CONTACTING SAID GAS OIL WITH A LIQUID SOLVENT COMPRISING FURFURAL AT A SOLVENT RATIO WITHIN THE RANGE OF ABOUT 120 TO 300 VOLUMES OF SOLVENT TO 100 VOLUMES OF SAID GAS OIL IN A SOLVENT EXTRACTION ZONE, WITHDRAWING EXTRACT MIX COMPRISING FURFURAL AND DISSOLVED HYDROCARBONS CONSISTING OF 70 TO 85 PERCENT AROMATIC HYDROCARBONS FROM SAID EXTRACTION ZONE AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 80 TO 100*F. WHILE MAINTAINING A TEMPERATURE GRADIENT THROUGH SAID EXTRACTION ZONE LESS THAN ABOUT 50*F., PASSING AT LEAST A PART OF SAID EXTRACT MIX TO A DISTILLATION ZONE IN CONTACT WITH A REFLUX AS HEREINAFTER PROVIDED AND ADDED STEAM AT A RATE OF ABOUT 0.1 POUND OF STEAM PER POUND OF EXTRACT MIX PASSED TO SAID DISTILLATION ZONE, DISTILLATIVELY SEPARATING AN OVERHEAD VAPOR COMPRISING AN AZEOTROPE OF WATER, FURFURAL AND HYDROCARBON FROM A BOTTOMS PRODUCT COMPRISING AROMATIC HYDROCARBONS OF AT LEAST 90 PERCENT BY VOLUME PURITY, CONDENSING SAID OVERHEAD VAPOR FORMING AN OIL-RICH PHASE, A WATER-RICH PHASE AND A FURFURAL-RICH PHASE, AND PASSING AT LEAST A PORTION OF SAID FURFURAL RICH PHASE AS SAID REFLUX TO SAID DISTILLATION ZONE. 